This invention relates generally to cargo inspection systems and, more particularly, to cargo inspection systems incorporating computed tomography (CT) to inspect cargo for contraband and methods for operating the same.
Since the events of Sep. 11, 2001, the Department of Homeland Security has increased security dramatically in U.S. airports. Such security efforts include screening passengers and carry-on bags and luggage for contraband including explosive materials.
Many of these systems employ single or few multi-view x-ray transmission technology. Although, these systems enable the detection of weapons and blades, for example, they lack the capability of detecting explosives with a low false alarm rate.
CT provides a quantitative measure of material characteristics, regardless of location or the superposition of objects; a substantial advantage over conventional and multi-view x-ray transmission and radioisotope-based imaging systems. In a CT scanner, a large number of precise x-ray “views” are obtained at multiple angles. These views are then used to reconstruct planar or volumetric images. The image is a mapping of the x-ray mass attenuation value for each volume element (or voxel) within the imaged volume.
Systems employing CT are widely employed in airports around the world in checked luggage to detect explosives that pose a threat to aviation safety. These systems employ an x-ray source and opposing detectors that rotate around a horizontal axis while the suitcase is translated along the same horizontal axis.
While such screening processes are also reliable and suitable for break-bulk cargo, there is a need for inspecting large crates, pallets and containers too large to inspect with conventional checked-luggage scanning systems. Further, it is too time consuming to remove and inspect the contents of each cargo container before loading the container for delivery to the destination. Only a portion of air cargo containers are inspected using currently available technologies including manual inspection, canine inspection and/or trace detection. It is recognized that these inspection methods must be improved for automation and/or to obtain greater detection.
Computed Tomography for objects larger than checked luggage requires a high-energy x-ray generator to penetrate the more attenuating objects and a large array of high-energy detectors to cover the large objects and detect the higher energy of the radiation.
Systems employing these principles are in use for Non-Destructive Testing (NDT) of machine parts, jet engines and rockets, for example. These systems are tailored for NDT applications with characteristics not suitable for contraband inspections. In addition, the scanning and image reconstruction processes are very slow.
A CT scanning system has been described that includes a rotatable table that supports a container and an x-ray source and an opposing x-ray detector that are movable parallel to the rotational axis of the table to scan cargo containers for the detection of explosives and other contraband.